1. Field of the Invention
The present invention relates to a method, system, and article of manufacture for synchronizing logical path resources.
2. Description of the Related Art
In certain computing environments, a host computer may communicate with a storage control unit, where the storage control unit controls physical storage. The physical storage that is controlled by the storage control unit may be represented logically as a plurality of logical path resources within the storage control unit. Applications in the host computer may perform input/output (I/O) operations with respect to the logical path resources of the storage control unit. For example, an application in the host computer may write to logical path resources of the storage control unit. The storage control unit may maintain a correspondence between the logical path resources and storage media in the physical storage via logical and physical volumes. While data may be physically written to the storage media in the physical storage under the control of the storage control unit, as far as an application in the host computer is concerned, the application performs write operations with respect to the logical path resources in the storage control unit.
Logical path resources may be added, deleted, or otherwise modified within the storage control unit. Certain modifications to the logical path resources of the storage control unit, such as addition of a logical path resource when no path resources are available, may cause a failure of I/O operations that are sent from the host computer to the storage control unit.
For example, to establish a logical path, a host sends an establish logical path message for each logical subsystem the host wants to access. Once a host establishes a logical path, the host can access all the devices in a logical subsystem. As long as the maximum number of logical paths per port has not been reached, a host may establish a new logical path on that port. However, when a maximum number of logical paths per port are reached, a host may not be able to establish new logical paths on that port. For each establish logical path rejected, a host receives an “Out of resources” status indication. In certain systems, to add a new logical path, an operator must remove an existing logical path from that port. Once the logical path has been removed from the port, the host may establish the new logical path. However, it is possible that the establishment of a new logical path from a host may fail again. The failure may occur because another host (e.g., an intervening host) has established a logical path. In this situation, the intervening host steals the logical path slot made available when the operator removed a logical path from the port.
Accordingly, it would be desirable to enable a host to directly replace logical path resources.